TBILISI, Georgia — U.S. Vice President Dick Cheney vowed on Thursday to stand by Georgia in its showdown with Russia, calling Moscow's military push into the ex-Soviet state an "illegitimate" act that cast grave doubt on its reliability.

Cheney, a hawk and one of Moscow's harshest critics, is the highest ranking U.S. official to visit Georgia since Tbilisi tried to retake the breakaway region of South Ossetia by force in early August and was overwhelmed by the Russian military.

His typically strong comments are likely to rile the Kremlin which has accused Washington of fuelling tensions by emboldening Georgian President Mikheil Saakashvili, a U.S.-educated lawyer with close ties to President Bush's administration.

"After your nation won its freedom in the Rose Revolution, America came to the aid of this courageous young democracy," Cheney told reporters, referring to the peaceful revolution in 2003 which brought Saakashvili to power.

"We are doing so again as you work to overcome an invasion of your sovereign territory and an illegitimate, unilateral attempt to change your country's borders by force that has been universally condemned by the free world," Cheney said, standing next to Saakashvili on his first visit to Tbilisi.

Cheney, on a tour of U.S. allies in the region that started on Wednesday in Azerbaijan, said Russia's actions had cast "grave doubt" on its intentions and reliability as a partner, both in the region and internationally.

Energy corridorBoth Azerbaijan and Georgia are links in the chain of a Western-backed energy corridor bypassing Russia which the West fears could be in jeopardy following the Kremlin's military thrust into Georgia.

Moscow has said it acted in Georgia to prevent what it called genocide when Tbilisi launched its military push into pro-Russian South Ossetia on August 7.

The Kremlin subsequently recognized South Ossetia and a second rebel region, Abkhazia, as independent states, drawing condemnation from Washington and Europe.

Only Nicaragua has followed Moscow's example on recognition and Russia's ex-Soviet security allies in the Collective Security Treaty Organisation stopped short of doing so, although they did blame Georgia for the conflict.

Russia has defied the West by keeping troops in a "buffer zone" on Georgian territory, a move the United States and European Union say violates a French-brokered peace plan. Moscow says the troops are needed to provide security and are not at odds with the ceasefire.

Few optionsCheney reiterated support for Georgia's bid to join NATO, calling it a defensive alliance that posed no threat to Russia.

He said he had also assured Saakashvili in one-on-one talks that lasted over an hour of the U.S. commitment to keeping the breakaway regions within Georgia. Cheney urged a peaceful resolution of the dispute, saying the long-term security of the region was at stake.

The United States has considered moves to punish Moscow for its intervention in Georgia, such as scrapping a lucrative civil nuclear deal, but it has not announced any sanctions and the West appears to have few options for influencing Russia.

On Wednesday, the United States announced an aid package of more than $1 billion to help Georgia rebuild housing, transportation and other infrastructure destroyed in its five-day war with Russia.

Washington is also sending the USS Mount Whitney, a sophisticated command warship of the U.S. Sixth Fleet, to Georgia loaded with over 17 tonnes of humanitarian aid -- a move the Kremlin sees as a dangerous game of Black Sea brinkmanship.

"America will help Georgia rebuild and regain its position as one of the world's fastest growing economies," Cheney said.

Saakashvili said Georgia had weathered a "terrible storm" and was ready now to plant "new seeds."

Ukraine visitBefore flying to Ukraine -- like Georgia an ex-Soviet country seeking NATO membership -- Cheney was briefed on humanitarian relief efforts and watched the unloading of a C130 transport plane carrying blankets, food rations and other supplies to the military section of Tbilisi airport, which was bombed by Russian forces last month.

U.S. officials say $37 million in U.S. humanitarian aid has arrived in Georgia since the war began last month.

Cheney's Ukraine visit comes at a time of significant political turbulence. President Viktor Yushchenko announced on Wednesday that Kiev's coalition government had collapsed and threatened to call a snap parliamentary election.

It would be the third election in as many years since the 2004 Orange Revolution swept Yushchenko to power on a promise of greater integration with the West.